Fiber optic communications are a technology area that is of crucial importance to U.S. High Technology industries. The 1990 Council on Competitiveness identified fiber optics as one of the key technology areas where U.S. industry is competitive in the world marketplace.
At present, the telecommunications industry is the largest user and developer of fiber optic products. However, the data communications industry is beginning to convert to fiber, and it is in data communications that the most growth potential is expected over the next 20 years. It is also expected that this growth will also be fueled by the emergence of ATM/SONET as a convergence of telecommunications and data communications (Ref. 5).
The optoelectronic telecommunications (opto telecom) industry developed the fundamental technologies to facilitate the emergence of the optoelectronic data communications (opto datacom) industry. There are, however, considerably different user requirements in these two industries that have driven the opto datacom product developers to expand on the telecom base technologies.
One of the most significant differences is that opto datacom is transceiver module and connector intensive, while opto telecom is cable length intensive. Currently, opto datacom is emerging more slowly than expected due to cost resistance for transceiver modules and connectors. Recently, the cost of opto datacom cables with duplex connectors has dropped below $100 with the introduction of the SC Duplex connector. We expect that current efforts by cable vendors will continue this cost reduction to the $50 range, especially with the recent introduction of plastic ferrules.
The transceiver module is another story. Projected costs are much too high to allow proliferation of this technology. Discussions that we have had with several optoelectronic suppliers indicate that a price of $150 per Gbit/s for a transceiver module will be needed for wide application of opto datacom and eventually fiber to the home. Currently, these modules are in the $600-800 range and economies of scale can only reduce this price range to $500-600.
Currently, the most expensive element in transceiver modules, typically approximately 60%, is the optical subassembly (OSA). The OSAs contain the optical transmitting and receiving devices and a lens to focus the light. Typically, there will be two--the Transmitting OSA (TOSA) and Receiving OSA (ROSA).
Of the two OSAs, the one that transmits light (TOSA) represents about 75% of the cost of the two OSAs, as the aligning of the light from the laser source is much more difficult than focusing the light from the fiber onto the receiver photo diode.
The current technology starts with an edge emitting laser and usually envelops it in two levels of packaging, requiring three separate and painstaking alignment steps.
In the first level of packaging the optical source is first packaged into a "TO" (transistor outline) can. The optical source is usually a semiconductor laser, but could be an LED. The resulting TO package has a block on which the source is mounted, and conductive leads to make the electrical connections. The TO package is hermetically sealed, with a glass window to let the light out. The alignment of the source is active and semi-precise.
The TO can is then aligned to a "selfoc.RTM." or "GRIN" lens in a second active alignment. The lens is needed because the laser spot size (mode-field diameter) is on the order of 1 micron, and very divergent. Without this lens the coupling of light into the optical fiber in the connector would be less than 5% efficient.
The lens and TO can combination is then actively aligned to the remainder of the TOSA body. The manufacturing process to produce the current TOSA design is highly labor intensive because of the three active alignments required.
Many of the parts in the connector are expensive machined stainless steel or ceramic. A concerted effort in reducing the levels of packaging and developing significantly less expensive opto packaging designs, materials and processes would competitively posture the U.S. to be in a leadership position in this important technology.